Abstract
Chronic adolescent exposure to Δ-9-Tetrahydrocannabinol (THC) is linked to elevated neuropsychiatric risk and induces neuronal, molecular and behavioural abnormalities resembling neuropsychiatric endophenotypes. Previous evidence has revealed that the mesocorticolimbic circuitry, including the prefrontal cortex (PFC) and mesolimbic dopamine (DA) pathway are particularly susceptible to THC-induced pathological alterations, including dysregulation of DAergic activity states, loss of PFC GABAergic inhibitory control and affective and cognitive abnormalities. There are currently limited pharmacological intervention strategies capable of preventing THC-induced neuropathological adaptations. L-theanine is an amino acid analogue of L-glutamate and L-glutamine derived from various plant sources, including green tea leaves. L-theanine has previously been shown to modulate levels of GABA, DA and glutamate in various neural regions and to possess neuroprotective properties. Using a pre-clinical model of adolescent THC exposure in male rats, we report that L-theanine pre-treatment prior to adolescent THC exposure is capable of preventing long-term, THC-induced dysregulation of both PFC and VTA DAergic activity states, a neuroprotective effect which persists into adulthood. In addition, pre-treatment with L-theanine blocked THC-induced downregulation of local GSK-3 and Akt signaling pathways directly in the PFC, two biomarkers previously associated with cannabis-related psychiatric risk and sub-cortical DAergic dysregulation. Finally, L-theanine powerfully blocked the development of both affective and cognitive abnormalities commonly associated with adolescent THC exposure, further demonstrating functional and long-term neuroprotective effects of L-theanine in the mesocorticolimbic system.SIGNIFICANCE STATEMENTWith the increasing trend of cannabis legalization and consumption during adolescence, it is essential to expand knowledge on the potential effects of adolescent cannabis exposure on brain development and identify potential pharmacological strategies to minimize THC-induced neuropathology. Previous evidence demonstrates that adolescent THC exposure induces long-lasting affective and cognitive abnormalities, mesocorticolimbic dysregulation and schizophrenia-like molecular biomarkers that persist into adulthood. We demonstrate for the first time that L-theanine, an amino acid analogue of L-glutamate and L-glutamine, is capable of preventing long-term THC side-effects. L-theanine prevented development of THC-induced behavioral aberrations, blocked cortical downregulation of local GSK-3 and Akt signaling pathways and normalized dysregulation of both PFC and VTA DAergic activity, demonstrating powerful and functional neuroprotective effects against THC-induced developmental neuropathology.
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